1. Field of the Invention
The present invention relates to an automatic dialysis method and apparatus.
2. Description of the Related Art
As is known in the case of patients undergoing a conventional haemodialysis treatment, collateral effects are often found to occur, which are characterized by slight hypotension phenomena or even by collapse phenomena.
These phenomena are caused by the fact that, for their operation, current dialysis apparatuses provide for the establishment of a set of predefined values and act on the patient in open loop, using no feedback information originating from the patient himself. In a significant percentage of cases, this leads to having clinical complications caused by the extreme variability in the capacity of the patient to withstand a given loss of weight.
In order to avoid these undesirable drawbacks, it is suitable to monitor certain patient parameters which indicate his state of health.
Previous inventions, for example, relate to apparatuses based on controlling the patient's blood volume, measured as the relative variation in the blood volume (BV) circulating in the body with respect to the start of the session, and control systems which can make the BV follow a predefined profile, with the aim of solving the problem of hypovolaemia which often occurs spontaneously. The percentage variation in the blood volume circulating in the body can be measured using several methods, for example the one described in patent TO91A000527 in the name of the Applicant Company, which, as a quantity indicating the patient's well-being, takes into consideration the cystolic blood pressure whose correlation with the BV is known.
Conversely, other inventions relate to apparatuses which control particular patient parameters, as stated, for example, in patent applications EP-A-029 793 and EP-A-089 003. In particular, patent EP-A-029 793 in the name of Thomasset describes a system comprising measurement of the impedance of the blood and an apparatus which injects sodium chloride into the patient when the measured impedance value departs from predefined thresholds. This system produces simple feedback of the stop/go type which is scarcely efficient from the clinical point of view.
In contrast, patent EP-A-089 003 in the name of TOYOTA CHUO KENKYUSHO describes an apparatus based on an elementary control system aiming to make the blood volume follow a profile which is fixed beforehand at the start of the treatment, on the basis of the condition of the patient. In this known system, the haematocrit is measured in order to obtain the variations in the blood volume. However, it is demonstrated that measuring the haematocrit is not sufficient for determining the variations in the blood volume, in so far as the assumption forming the basis of the one-to-one relationship between the haematocrit and the variation in the blood volume, that is to say the assumption of constant total cell volume, is rarely satisfied. In any case, the proposed type of control is not suitable for application to an entire population of patients or to different sessions for a single patient, or even to different times during the same session, since it does not take into account the individual reactions to the treatment, which not only are generally different from one patient to another but may also vary for the same individual at different times. Furthermore, the limitations to which the machine parameter manipulation is subject are not taken into account in this patent. This is why the described system is ineffective if there are significant variations in the patient's intradialysis behaviour pattern.
An aspect which has not yet been resolved in any existing dialysis system is the full harmonization of different clinical objectives, to obtain which it is constantly necessary to make compromises between expediently obtaining a result, for example the final weight loss (TWL) which contributes to maintaining the patient's conditions of well-being in the medium and long term, and the final reduction in the blood volume (TVB) which allows intradialysis haemodynamic stabilization with, a consequent reduction in pathology during treatment. In traditional dialysis, the clinical evaluation relating to this compromise is made approximately by the doctor who, for each individual dialysis, chooses the treatment parameters which he adopts, on the basis of his own experience after having determined their effects on the patient, for example the weight loss rate (WLR) defined as the difference between the ultrafiltration rate (UFR) and the transfusion rate (Q.sub.inf), the conductivity of the dialysis fluid (CD), and may possibly have to review his choice during the treatment subsequent to collapse phenomena.
However, in the automatic dialysis system which is mentioned, this compromise must still be made by hand during the phase of prescribing the treatment, and the situation must be reviewed during the treatment in accordance with the impossibility of simultaneously obtaining the relevant point objectives. This discontinuous management of the dialysis treatment has the effect of partially offsetting the advantages obtained by the automatic system. This is because performing automatic dialysis using the methods mentioned requires great experience in formulating the prescription in the form of desired profiles, and quick intervention if the prescription is inappropriate or cannot be continued because of the patient's contingent conditions.